Microwaves are electromagnetic energy waves with very short wavelengths, typically ranging from a millimeter to 30 centimeters peak to peak. In high-speed communications systems, microwaves are used as carrier signals for sending information from point A to point B. Information carried by microwaves is transmitted, received and processed by microwave circuits.
Packaging of RF and microwave microcircuits has traditionally been very expensive. The packaging requirements are extremely demanding—very high electrical isolation and excellent signal integrity through gigahertz frequencies are required. Additionally, IC power densities can be very high. KQ dielectric materials from HERAESUS has found favor among designers of microcircuits because of its ability to provide such high electrical isolation while using more forgiving thick film processes.
One are in which the use of KQ has caused problems is the inability to create certain useful via structures. A typical layer of KQ is about 5 mils ({fraction (5/1000)}th of an inch) thick. It is difficult to constructing vias through 5 mils of KQ that terminate on, but not pierce, a ground plane on top of a substrate. Another problem is that, to obtain a desired 50 ohm impedance in the signal path, the width of each via should be between 30 and 40 mils. An additional 20 mils of space is desirable to provide sufficient signal isolation. In the context of interconnecting an IC, this results in a rather large pitch. Accordingly, an interconnection scheme is needed that maximizes available real estate on the substrate.
The present inventors have recognized a need for method and apparatus for replicating the functionality of vias while maximizing the use of space on a substrate.